The present invention relates to material for purification of physiological liquids of organism.
It is well known that physiological liquids of organisms such as blood, plasma, peritoneal liquid etc., accumulate and transport various toxicants in the case of poisoning the organism as well as in the case of diseases, in particular diseases of liver and kidneys. It is therefore advisable to remove the toxicants from the physiological liquids to significantly improve the situation of the patient. A plurality of methods have been invented and have been utilized for removing toxicants from blood, plasma and other physiological liquids. One of the most efficient methods is hemodialysis. This method, however, is generally restricted to removing small toxic molecules, whereas toxins belonging to the so-called middle-size molecules (between 500 and 30000 Dalton molecular weight) are eliminated too slowly, even with modern xe2x80x9chigh fluxxe2x80x9d dialyser membranes. It is believed to be advisable to further improve the existing methods so as to provide an efficient purification of the physiological liquid of organism, especially with respect to above toxicants having larger molecular sizes, for the purpose of preventing propagation of diseases or curing the disease. Some solutions were disclosed in our earlier patent application Ser. No. 08/1756,445, now allowed U.S. Pat. No. 5,773,384.
Accordingly, it is an object of present invention to provide a material for purification of physiological liquids of organism, which is a further improvement in the above specified field.
In accordance with present invention, the material for purification of physiological liquids of organism is proposed, which material has a size, a shape, and a structure selected so as to remove toxic compounds from the physiological liquid and is composed of a partially chloromethylated porous highly crosslinked styrene or divinylbenzene copolymer which initially have surface exposed chloromethyl groups in which thereafter chlorine is replaced with an element which forms different surface exposed functional groups with a greater hydrophilicity and greater biocompatibility than that of the chloromethyl group.
In accordance with a preferable embodiment of the present invention, the pore size of the material is selected as being in the range between 1 and 15 nm and the structure of the material is selected such that hydrophobic surface in the above pores should be exposed to middle-size molecules. Thus, hydrophobic microporous and mesoporous polymeric materials are best suited for removing toxicants such as for example beta2 microglobulin and others. These materials may also contain transport-enhancing macropores which surface, however, must be made biocompatible, just like the other surface of the polymer material. When the method is performed in accordance with present invention, it provides for an efficient removal of broad range of toxicants from blood, plasma and other physiological liquids of organism.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments.
In accordance with present invention, a purification of physiological liquids of organism by removing toxicants, and other physiological liquids of organism from blood is proposed. A patient""s blood is withdrawn from an arterial blood circulatory access point, past through a polymer which removes toxicants, and re-enters the patient through a venous access point. The polymer has such a pore size and a structure which provides the removal of beta-2 microglobulin. More particularly, the pore size of the polymer is within the range 1-15 nm.
The polymers impression can be styrenic, acrylic, or any other polymers satisfying the above mentioned conditions.
One example of the material through which the blood can be passed for purification of physiological liquids of organism is a sorbent for removing toxicants from blood or plasma, which has a plurality of beads of hypercrosslinked polystyrene resin, which beads have a surface modified so as to prevent adsorption of large proteins and platelet and to minimize activation of blood complement system, without affection noticeably the accessability of the inner adsorption space of the beads for small and middle-size toxicant molecules.
To achieve the desired chemical modification of the bead surface, which are intended to enhance the hemocompatibility of the material, one possible approach is the formation of lipid-like layers on the surface of polystyrene beads, which should simulate the structure of biomembranes. Copolymers of 2-methacryloyloxyethyle-phosphorylcholine with n-butyl-methacrylate can be grafted on the surface of materials. The copolymer was shown to adsorb free phospholipids from blood to form an organized structure similar to that of a bilayer membrane. It is believed that membrane-like surfaces are thus formed which reduce adsorption of proteins and platelet from blood and make the material more biocompatible. In our approach, groups of phosphatidylcholine are formed on the surface of polystyrene beads, without a preliminary grafting of the hydrophilic copolymer suggested by Ishihara, et al.
Second approach consists of depositing heparin on the surface of the polystyrene beads. This can be done in several ways, including (I) chemical covalent binding of heparin to the polystyrene chains on the surface of beads, or (ii) electrostatic adsorption of heparin molecules, which are negatively charged, to positively charged ionogenic groups introduced into the surface layer of the beads. Heparin inhibits activation of the blood complement system and prevents formation of clots.
Still another approach consists of binding long hydrophilic polymer chains on the beads surface, which should prevent contacts between blood proteins and cells with the hydrophobic polystyrene surface.
Finally, the fourth approach is depositing high molecular weight fluorinated polyalkoxyphosphazene on the outer surface of the beads. Phosphazene represents the best biocompatible polymeric material. Modification of the sorbent surface consists in contacting the polystyrene beads with an appropriate amount of a solution of the polyphosphazene in an organic solvent. Due to the ability of the hypercrosslinked polystyrene to strongly swell with the solvent, the latter appears completely incorporated into the beads after a short period of time, whereas the dissolved polyphosphazene remains deposited on the surface of beads. The solvent incorporated into the beads is then removed by heating the beads under reduced pressure. The large size of polyphosphazene molecules used in this procedure prevents their penetration into the pores of the beads. Therefore, the whole of the internal surface of the material remains active and accessible to blood toxicants, whereas the outer surface exposes to blood proteins and cells the insoluble in water and biocompatible polyphosphazene.
The chemical modification of the surface of sorbent beads, which is the case in the first three of the above modification approaches, is facilitated by the remarkable peculiarity of the hypercrosslinked polystyrene, namely, that the reactive functional groups of the polymer are predominantly located on its surface. The hypercrosslinked polystyrene is generally prepared by crosslinking polystyrene chains with large amounts of bifunctional compounds, in particular, those bearing two reactive chloromethyl groups. The latter alkylate, in a two step reaction, two phenyl groups of neighboring polystyrene chains according to Friedel-Crafts reaction with evolution of two molecules of HCl and formation of a cross bridge. During the crosslinking reaction, the three-dimensional network formed acquires rigidity. This property gradually reduces the rate of the second step of the crosslinking reaction, since the reduced mobility of the pending second functional group of the initial crosslinking reagent makes it more and more difficult to find an appropriate second partner for the alkylation reaction. This is especially characteristic of the second functional groups which happen to be exposed to the surface of the bead. Therefore, of the pending unreacted chloromethyl groups in the final hypercrosslinked polymer, the largest portion, if not the majority of the groups, are located on the surface of the bead (or on the surface of large pores). This circumstance makes it possible to predominantly modify the surface of the polymer beads by involving the above chloromethyl groups into various chemical reactions which are subject of the present invention.
The following examples are intended to illustrate, but not to limit, the invention. In general, the examples and associated preparation protocols illustrate the modification of the surface of microporous and biporous hypercrosslinked polystyrene beads prepared by an extensive crosslinking of corresponding styrene-divinylbenzene coppolymers using monochlorodimethyl ether as the bifunctional reagent or using other conventional chloromethylation and post-crosslinking protocols. The content of residual pending chloromethyl groups in the polystyrene beads amounts to 0.5-1.0% CL for the microporous and up to 7% for biporous materials. The beads of the initial material should preferably be spherical and smooth to minimize possible damages to hematocytes.
The sorbents prepared in accordance with this invention are charged to a column or cartridge for service. The column should preferably be provided with an inlet and an outlet designed to allow easy connection with the blood circuit, and with two porous filters set between the inlet and the sorbent layer, and between the sorbent layer and the outlet. The column may be made of a biocompatible material, glass, polyethylene, polypropylene, polycarbonate, polystyrene. Of these, polypropylene and polycarbonate are preferred materials, because the column packed with the sorbent can be sterilized (e.g., autoclave and gamma-ray sterilization) before use.
The column or cartridge is then filled with a 1% solution of human serum albumin in normal saline and stored at 4xc2x0 C. When ready for use, the column is washed with 0.9% NaCl solution to which has been added a suitable anticoagulant. such as ACD-A containing heparin in an effective amount. For a 250 ml cartridge, this is approximately 11 of the sodium chloride solution to which 150 ml of ACD-A containing 6,000 units of heparin has been added.
As usual the following two typical extracorporeal blood circulation systems can be employed:
(I) Blood taken from a blood vessel of a patient is forced to pass through a column packed with the sorbent of this invention, and the clarified blood is returned to the blood vessel of the patient.
(ii) Blood taken from a patient is first separated through a separation membrane by centrifugation or the like into hemocytes and plasma, the plasma thus separated is then forced to pass through the column packed with the sorbent of this invention to remove toxicants from the plasma; then, the clarified plasma from the column is mixed with the hemocytes separated above, and the mixture is returned to the blood vessels of the patient.
Of these two methods, the latter is more practical because of the smaller loss of hemocytes, for example, by adhesion of platelets and erythrocytes
Any other ways of performing hemoperfusion or plasma perfusion are appropriate with the modified sorbents of this invention. Especially promising seems to be the above mentioned suggestion of Bodden (U.S. Pat. No. 5,069,662, December 1991), by which high concentrations of anti-cancer agents are perfused through the liver or other body organ containing a tumor and then the effluent blood is subjected to the extracorporeal hemoperfusion to remove the excess of the drug before the blood is returned to the blood circulation system of the patient. Another perspective system is that by Shettigar, et al. (U.S. Pat. No. 5,211,850, 1993), where achieving both convective and diffusive transport of plasma across a hollow fiber membrane towards a closed chamber with a sorbent and back into the fiber channel was suggested2E. The chamber could be packed with the sorbent of this invention.
In general, the modified hypercrosslinked polystyrene sorbents of the present invention are intended to replace in hemoperfusion and plasma perfusion procedures all kinds of activated carbons. The new material is mechanically stable and does not release fines causing embolia; it is much more hemocompatible, exhibits higher sorption capacities toward a broad range of blood toxicants, and can, in principle, be regenerated and reused.
The adsorption spectrum of modified hypercrosslinked polystyrene sorbents of this invention extends to substances with molecular weights of between 100 and 20,000 daltons. The maximum adsorption is of molecules with weight of between 300 and 5,000 daltons, identified clinically as xe2x80x9cmedium moleculesxe2x80x9d, which are present in abnormal quantities in ureamic and many others patients and are incompletely removed by conventional hemodialysis procedures. Such compounds as creatinine, barbiturate, phenobarbital, sodium salicylate, amphetamines, morphine sulfate, meprobamate, glutethimide. etc. can be effectively and rapidly removed from the blood using both microporous and biporous sorbents. (To avoid removal of useful drugs from blood during hemoperfusion on the new sorbents, the latter can be previously saturated with the corresponding drug to an appropriate level). In addition to removal of small and medium molecules, the biporous sorbents also shows an excellent ability to absorb cytochrom C and beta-2-microglobulin(molecular weight of about 20,000 daltons) as well as vitamin B12.
Preparation of initial hypercrosslinked polystyrene to a solution of 87.6 g xylylene dichloride (0.5 mol) in 600 ml dry ethylene dichloride 104 g (1 mol) of styrene copolymer with 0.5% divinylbenzene were added, the suspension was agitated for 1 hr and supplied with a solution of 116.8 ml tinn tetrachloride (1 mol) in 100 ml ethylene dichloride. The reaction mixture was then heated for 10 hrs at 80xc2x0 C., the polymer was filtrated and carefully washed with aceton, a mixture of aceton with 0.5 N HCl, 0.5 N HCl and water until no chlorine ions were detected in the filtrate. The product dried in vacuum represented microporous hypercrosslinked polystyrene. It contained 0.65% pendant unreacted chlorine and displayed an inner surface area as high as 980 m2/g.
To a suspension of 104 g (1 mol) of a macroporous styrene copolymer with 4% divinylbenzene in 500 ml dry ethylene dichloride a solution of 76 ml (1 mol) monochlorodimethyl ether and 116.8 ml (1 mol) tinn tetrachloride (1 mol) in 100 ml ethylene dichloride was added. The mixture was then heated at 80xc2x0 for 10 hrs, the polymer was filtrated and carefully washed with aceton, a mixture of aceton with 0.5 N HCl, 0.5 N HCl and water until no chlorine ions were detected in the filtrate. The product dried in vacuum represented biporous hypercrosslinked polystyrene and contained 3.88% pendent unreacted chlorine. The above extensive crosslinking resulted in the increase of its inner surface area from 120 to 1,265 m2/g.
Formation of Lipid-like Surface Structures